Improvements relating to lenses

ABSTRACT

A method of forming a polymer is disclosed. The method comprises: positioning a mould in relation to a bath containing a molten material to form a mould cavity between the mould and the molten material; adding a monomer within the mould cavity; and curing the monomer to form a polymer.

TECHNICAL FIELD

The present invention relates to improvements in the manufacture andevaluation of lenses. More specifically, it relates to lenses formedusing a monomer material cast between two forms.

BACKGROUND ART

Lens formation can be a complicated process. This is especially the casewhere lenses are formed in a layered manner using a film or foil, suchas PMMA, and a cast lens material, such as a UV-curable monomer. Castlenses with embedded films can be produced applying the method disclosedin WO2018/087011 A1. Known processes for lens formation are limited tocasting between two solids, or between a solid and a gas, for exampleair, or a vacuum. Such processes have many drawbacks, which the presentapplication seeks to overcome.

STATEMENTS OF INVENTION

According to a first aspect, there is provided a method of forming apolymer, comprising:

-   -   positioning a mould in relation to a bath containing a molten        material;    -   adding material between the mould and the bath; and    -   curing the material to form a polymer.

The invention therefore provides for an improved method of forming apolymer that provides an enhanced surface finish on one surface of thepolymer. It is considered that the word “mould” can include not onlymoulds that are not intended to be a part of a final product and aretherefore to be discarded, but also substrates that are intended to be apart of a final product.

The method may further comprise a step of solidifying at least part ofthe molten material after curing the monomer. The solidified at leastpart of the molten material may form a handle, holder, or protectivecasing. By solidifying some or all of the molten material, it may beeasier to both transport the polymer with or without the attachment ofthe mould. For example, the solidified material may provide protectionand/or rigidity to the polymer.

The mould may be positioned using a flotation device that is supportedby the molten material and that is configured to hold the mould in a setposition relative to the molten material. The use of a flotation deviceensures that the mould is held level relative to the surface of themolten material and at a desired angle that is set by the connectionbetween the mould and the flotation device. The flotation device may betoroidal or ring-shaped. Alternatively, the flotation device may takeany other shape.

The flotation device may be rigidly connected to the mould and may forma part of the mould. For example, the flotation device may form one ormore walls of the mould, such as the side walls, whilst the mould formsother walls, such as an upper wall that interconnects the side walls.The mould and flotation device may be integrally formed as onecomponent.

The mould may be adjustable in position relative to the flotationdevice. The mould may be moveably connected to the flotation device suchthat a user can adjust the position of the mould relative to theflotation device. Thus, whilst the flotation device remains fixed inposition relative to the molten material, the mould may be movedrelative to the molten material to change the shape and/or size of themould cavity, i.e. the space between the mould and the molten material.The shape and size may be changed, for example, by altering a verticaldistance between the mould and the molten material or by altering anangle of the mould relative to the molten material. The adjustabilitymay be provided by any form of adjustment device including, for example,moveable joints such as ball and socket joints, hinges, sliders,ratchets, etc.

The method may further comprise the step of adjusting the position ofthe flotation device relative to the molten material by adding orremoving ballast on the flotation device. This may be considered to be apart of the step of positioning the mould relative to the moltenmaterial. Ballast may be applied evenly over the flotation device inorder to raise or lower the flotation device in the molten material,i.e., to adjust its overall buoyancy. Alternatively, ballast may beapplied unevenly over the flotation device in order to alter itsorientation relative to the molten material, i.e., to adjust its localbuoyancy.

The step of adding the monomer may be executed through ports in themould and/or flotation device. By adding the monomer through ports, themonomer may be added with the mould cavity in its intended positionrelative to the molten material. The mould may be tilted whilst themonomer is added. Where a flotation device is also used, the mouldand/or the flotation device may be tilted. This may assist with theavoidance of bubbles or air gaps within the mould cavity. For example,the tilting of the mould may allow the monomer to be added to a portthat is tilted to be lower than its resting position whilst allowing airor gas within the mould cavity to escape through a port that is tiltedto be higher than its resting position.

The method may further comprise the step of forming a surface pattern onthe molten material prior to the curing of the monomer. By forming apattern on the surface of the molten material, the pattern may betransferred to the monomer when it cures, making a pattern on the curedpolymer. The surface pattern may be formed by way of an ultrasonicemitter. The ultrasonic emitter may be applied such that it directsultrasonic waves through the molten material and may, for example, bepositioned at an edge of the bath.

The method may further comprise the step of embedding an object in themonomer, prior to curing. The object may be embedded on the surface ofthe monomer or may be embedded within the monomer. The object may bepositioned by way of one or more spacers. The object may be, forexample, a foil, hologram, decorative element (e.g. jewellery, logos,etc.), electronic component, or other such object.

The method may further comprise the step of positioning, prior to curingof the monomer, a secondary mould that bounds the mould cavity, thesecondary mould being supported by the molten material. The use of asecondary mould may allow the creation of a greater variety of polymershapes.

According to a second aspect of the invention, there is provided asystem for forming a polymer, the system comprising:

-   -   a bath containing a molten material; and    -   a mould positioned in relation to the bath in order to form a        mould cavity between the mould and the molten material, for the        receipt of a monomer.

The system may further comprise a flotation device that is supported bythe molten material and is configured to hold the mould in a setposition relative to the molten material.

The mould may be adjustable in position relative to the flotationdevice. The flotation device may comprise a support structure includingone or more joints to allow the adjustment of the position of the mould.

The system may further comprise ballast that is movable to adjust theposition of the flotation device relative to the molten material.

The mould and/or flotation device may include ports for the addition ofmonomer.

The system may further comprise a device configured to form a surfacepattern on the molten material. The device may comprise an ultrasonicemitter.

The system may further comprise a secondary mould that bounds the mouldcavity, the secondary mould being supported by the molten material.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments will now be described in detail with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic view of a first assembly for moulding a lens;

FIG. 2 is a flow chart of a method for moulding a lens;

FIG. 3 is a schematic view of a second assembly for moulding a lens;

FIG. 4 is a schematic view of a third assembly for moulding a lens;

FIG. 5 is a schematic view of a fourth assembly for moulding a lens,including surface patterning;

FIG. 6 is a schematic view of a fifth assembly for moulding a lens,including embedding of an object on the lens surface;

FIG. 7 is a schematic view of a sixth assembly for moulding a lens,including embedding of an object within the lens; and

FIG. 8 is a schematic view of a seventh assembly for moulding a lens.

DETAILED DESCRIPTION

Known methods of forming polymer lenses utilise two super-polishedmoulds—often made of glass but which may also be made of carbide, etc.(in case of thermal curing)—that are aligned together. Liquid monomercan be inserted between the moulds and then hardened using UVirradiation in order to form a lens. With this process, separation ofthe lens from the mould is a known problem, as has been noted in theabove sections. In particular, separation of the mould from the lens cancause deformation of the lens, or may damage the mould and/or lens. Aspolishing is often an expensive process, the mould is often aconsiderable price factor. The method described below reduces the numberof polished moulds that are required by a factor of two.

It may be beneficial for the described methods to be utilised to castproducts where at least one of the sides is flat, and/or to be usedwhere the monomer is to be formed without embedded objects (such asfoil, holograms, jewellery, logos, electronics), either inside or on thesurface. There is also potential for the disclosed method to be used tocast something on a substrate (mould) without the intention of removingthe substrate (mould), for example in surface coating or laminating.

In particular, the described method may be used to form a plano-conex,plano-concave, or bi-plano lens, or to laminate such a layer on a UVtransparent substrate, with several advantages. Furthermore, not onlyflat but also certain patterns are possible.

Whilst the present method may be considered to be similar to float glassproduction, where a molten metal such as tin is used as a high surfacequality support for a molten glass, known method of float glassproduction are not suitable for the organic polymers commonly used toproduce optics. This is at least partly due to the high temperaturesinvolved, which are prone to damage the organic material and/or triggerpolymerisation earlier than is intended.

The disclosed method of forming the lens includes the use of alow-melting point metal, alloy, or other material in order to form amolten bath 102 on which the lens can be formed, as shown in FIGS. 1 and2 . Example low-melting point materials include Woods metal, Fieldsmetal, Cerrolow®, gallistan, and NaK. Other materials may also besuitable, such as mercury, although these may have downsides such ashigh toxicity. By using this method, fewer moulds may be required. Itmay even be possible to provide the method without a top mould, suchthat the lens is simply formed on the surface of the molten bath. Themolten bath may be used in conjunction with a UV-curable orthermally-curable monomer, resulting in at least one good qualitysurface on the side of the resulting cured sample that was in contactwith the molten material.

The softness of the molten metal bath allows the casting of even afragile object on a substrate—i.e. the top mould—even if the substratewere to be too soft or fragile to survive the traditional demouldingprocess. In one example, the polymer material may be only 200 micronsthick with an diameter, hence its fragility. This is equally applicablewhen it is desired to laminate a fragile material on a lens, forexample, where the removal of two moulds could lead to damage,especially if it is not clear which mould is to be removed first.

The assembly 100 is shown in FIG. 1 and a flow chart outlining themethod is shown in FIG. 2 . A mould 104 can be positioned S10 relativeto the molten bath 102 and then the monomer 106 can be filled S12between the molten bath 102 and the mould 104, whereupon the monomer 106may be cured S14, for example by the application of UV light or byincreasing the temperature (thermal curing). After curing, the monomer106 will be referred to as the sample. The assembly 100 of FIG. 1 alsoincludes spacers 108 that are used to enclose the sides of the monomer106 as well as to ensure correct spacing between the surface of themolten bath 102 and the mould 104. In some cases, it may also bedesirable to use an inert gas atmosphere and/or clean the molten metalsurface from impurities or oxides prior to filling the mould cavity 110with monomer. Once cured, the lens, i.e. the cured monomer 106, can beremoved from the mould 104 by applying any traditional method.Alternatively, the metal 112 making up the molten bath 102 may be cooleddown to allow better demoulding on the mould side. For example, bycooling the metal until it solidifies S16, the metal may hold the curedsample in order to enable removal from the mould S18, i.e. by forming ahandle. Once removed, the metal may be reheated to allow easy removal ofthe sample from the metal S20. After removal of the sample, the metal112 may be cleaned, allowing its re-use.

The steps of solidifying the metal 112 after the curing of the samplehas multiple benefits. For example, the solidified metal can act as aneasily removed grip or handle for the sample. This can allow the mould104 to be simply removed from the other side of the sample, for example,or can serve as protection for transport or downstream processing of thesample. This may be especially useful if the cured sample is thin orotherwise fragile.

As a sidenote to this, it is noted that some metals that could be usedfor the molten bath 102, such as bismuth-containing alloys, may expandupon cooling or solidifying. It is noted that this volumetric behaviourcould be ‘tuned’ to prevent sample deformation or to utilise thedeformation to provide a desired bend in the sample.

Normally, during curing, the monomer shrinks, along with any adhesivesused. This is known to produce stresses within the polymer sample, e.g.,the lens being produced, and stresses between the sample and the mould.The stresses may lead to partial detachment and therefore an unevensurface on the sample. Similarly, metals commonly shrink upon coolingand solidification. By using metals that do not act is this common way,the method can benefit from preventing or limiting the introduction ofthese stresses.

It may also be possible to utilise these effects in order to causedesirable bending of the sample. For example, the expansion of the metalupon cooling and solidifying, if designed to do so, could lead tobending of the sample. If the opposing side of the sample could then bepolished and then the sample released from the metal, the sample couldrebound to its previous shape, causing a lens shape to be formed. Thismay be desirable in some embodiments.

In some cases, the side of the lens that was in contact with the moltenbath may require cleaning, by the use of chemicals or otherwise. Thismay be particularly advantageous where the material making up the moltenbath 102 has an affinity for the surface of the lens, i.e. where theliquid wets the surface of the lens.

Different arrangements of the mould 104 with the molten bath 102 may beprovided and some additional examples are shown in FIGS. 3 to 8 .

FIG. 3 shows an embodiment 200 that utilises a self-levelling principlein order to correctly form the desired cured sample. The mould 204 isattached to a support structure 214 that comprises multiple adjustableparts and a flotation device 216. In FIG. 3 , the flotation device 216is formed as a torus of a material that floats on the molten metal 112.The support structure 214 includes a height adjustment means 218 and anangle adjustment means 220 that allows the user to adjust the positionof the mould 204 relative to the support structure 214 and therefore,due to the fact that the flotation device 216 will always be seated onthe surface of the molten bath 202, to adjust the position of the mould204 relative to the molten bath 202. In this way, the flotation device216 ensures that the mould 204 is always held in the desired positionfor creating the desired monomer sample, i.e. the mould 204 and supportstructure 214 is self-levelling. Although described as a torus, theflotation device may take many different shapes. In some embodiments, itmay be desirable to form the flotation device as a ring, for ease of useand manufacture. However, the flotation device may be a single part,such as a ring, or formed in multiple parts in any other shape.

It will be seen from FIG. 3 that, when the mould is in the angledposition, some of the mould may be under the surface of the moltenmetal. This may be undesirable, for example because it will have its ownbuoyancy and could affect the level of the flotation device or it couldresult in some bending of other components, especially when such anarrangement is used in conjunction with a foil or other object to beembedded within the monomer, as described below. In these situations, itmay be desirable to trim the part of the mould that is protruding intothe molten metal in order to limit the total amount of mould thatprotrudes, thus limiting or preventing these issues.

It can therefore be seen that the use of a molten bath 202 in themanufacture of cured monomer samples is not only useful in that it canproduce a high surface quality on the surface of the sample facing themolten metal 212, but also that it allows the upper mould 204 to beprecisely aligned when used with a buoyant flotation device 216. Thisbuoyancy also allows the self-levelling of the mould 204, to a designedangle, if desired.

FIG. 4 shows a further embodiment 300 that utilises the self-levellingprinciple in a similar way to that of the assembly of FIG. 3 . Here, thesupport structure is replaced with a simpler mechanism, whereby themould 304 is connected directly to the flotation device 316, which mayalso form a part of the mould 304, e.g. the spacer at the side of themould cavity. Due to the simpler nature of the assembly 300, the mouldcavity 310 may be adapted by altering the flotation characteristics ofthe flotation device 316. For example, by adding or removing ballastevenly over the flotation device 316 and/or mould 304, the flotationdevice 316 and mould 304 can be made to sit lower or higher in themolten metal 312, respectively. The eventual size of the monomer sampleproduced by the mould 304 can therefore be tuned as desired. Similar, byadding or removing ballast from the system unevenly, e.g. more ballaston the left of the flotation device 316 and less on the right, theflotation device 316 can be made to sit unevenly in the molten bath 304,i.e. for parts of the flotation device 316 to be seated lower in themolten bath 302 than other parts of the flotation device 316. In thisway, the overall thickness and the angle of the bottom of a curedmonomer sample can be adjusted by altering ballast placed on theflotation device 316 and/or mould 304.

In some embodiments, the mould may be separated from the flotationdevice. This may be useful when the upper surface is not required to bemoulded or after curing when the flotation device may then act as a lensholder, holding the cured sample for removal from the molten bath.

Also shown in FIG. 4 are ports 322 that extend through the flotationdevice 316 to provide access to the mould cavity 310. These ports 322can be used for venting and/or filling the mould cavity. In the depictedembodiment, two ports 322 are provided, which are in opposing positionsacross the mould cavity 310. This arrangement of the ports 322, alongwith other arrangements where the ports 322 are not adjacent to oneanother, can provide advantageous effects when using one port 322 forfilling and another for venting. For example, by angling the flotationdevice 316 and mould 304 such that the filling port is lower than theventing port, bubble formation may be limited or prevented. The portsmay also be allowed to be bigger than the would otherwise be possible inmore usual arrangements for creating polymer lenses. In furtherembodiments, it may be possible to place the monomer on the molten metaland then to position the mould and flotation device around the monomer,such that the monomer may flow into the mould or be drawn into themould, for example by surface tension. This may allow quicker filling ofthe mould.

FIG. 5 shows a further embodiment 400 whereby a surface pattern may becreated on the surface of the sample that is on the side of the moltenmetal 412. The assembly 400 is similar to that of FIG. 1 , butadditionally includes an ultrasound generator 424 that acts to create asurface wave pattern 426 in the molten metal 412. Other forms of wavegeneration may also be used and will be known to the skilled person. Inone embodiment, as shown, the ultrasound generator 424 emits a frequencysuch that a standing wave is formed in the top of the molten metal 412.The formation of the standing wave results in an imprint of the patternon the monomer, which can then be cured in order to retain the surfacepattern on the sample when removed from the mould 404. Of course, byvarying the application of the ultrasound, such as by changingfrequency, amplitude, or phase of one or more ultrasoundheads/generators 424, the surface pattern may be caused to form anynumber of different patterns. Such design is known in the art.

FIGS. 6 and 7 show arrangements 500, 600 that are again similar to thatof FIG. 1 , but additionally include an object 528, 628 that is to beembedded in the monomer sample, once cured. In the depicted embodiments500, 600, the object 528, 628 is a foil, but the object 528, 628 mayalso include other objects such as a holograms or other such objectsmentioned previously.

In FIG. 6 , the object 528 is positioned on the surface of the moltenmetal in order that, once the monomer 506 is cured, the object 528 willbe on the surface of the sample. Conversely, the object 628 in FIG. 7 ispositioned within the monomer 606 itself. The object 528, 628 may bepositioned such that it is floating freely within or upon the monomer506, 606, prior to curing, or spacers may be used that hold the object528, 628 relative to the mould 504, 604, in the desired position withinthe monomer 506, 606. The position may of course be controlled in bothlateral and vertical directions, whichever method is used to hold theobject.

FIG. 8 depicts a further embodiment 700 whereby two moulds 704 a, 704 bare positioned on the molten metal. A larger mould 704 a is positionedaround a smaller mould 704 b, creating a mould cavity 710 that isenclosed by the moulds 704 a, 704 b and the molten bath 702. Each of themoulds 704 a, 704 b include integrally a flotation device such that theyare each independently self-supporting on the molten metal 712. In thisway, the monomer 706 can be injected between the moulds 704 a, 704 b inorder to be shaped. The thickness of the monomer 706 can be adjusting byadding or removing ballast (not shown) from one or both flotationdevices in order to adjust how each sits within the molten metal 712. Insome embodiments, it may also be desirable to ensure accuratepositioning of the smaller mould 704 b within the larger mould 704 a bythe use of one or more spacers. It is also possible to combine thisembodiment with the teachings related to FIGS. 6 and 7 in order toposition a foil or other object on or within the monomer 706.

Of course, while the embodiment of FIG. 8 may not result in a reducednumber of moulds when compared with alternative methods of manufacture,the other benefits of the invention will still apply.

Whilst the disclosed method may be particularly useful in the case wherethe sample is to be removed from the mould, such as in lens manufacture,it may also be used in other circumstances. For example, the methodcould be utilised to allow coating or laminating of a sample over asubstrate, for example where the mould as shown in the Figures is asubstrate that is not intended for removal. This may be particularlyuseful in applications such as the manufacture of waveguides, microwavecircuits, pneumatic/fluidic circuits, stamps, etc. When used inconjunction with UV curing, for example, the present technique providessimilar imaging techniques to be used as with lithography, i.e., theprinting of complex patterns. In addition, the present technique mayallow a better surface finish and a larger thickness of the end samplethan would be possible using lithography.

It will be clear that, unless specifically stated otherwise, any one ormore features disclosed in relation to one embodiment of the inventionmay be used in conjunction with any one or more features from any otherembodiment or embodiments of the invention. For example, theself-levelling features of the embodiment of FIG. 3 may be used inconjunction with the foil position of the embodiments of FIGS. 6 and 7and/or an additional mould as in the embodiment of FIG. 8 . As a furthernon-limiting example, any of the embodiments may be combined with thesurface patterning feature of the embodiment of FIG. 5 . This applies toeach and every embodiment and is not limited to the specific examplesdiscloses herewith.

1. A method of forming a polymer, comprising: positioning a mould inrelation to a bath containing a molten material to form a mould cavitybetween the mould and the molten material; adding a monomer within themould cavity; and curing the monomer to form a polymer.
 2. The method ofclaim 1, further comprising a step of solidifying at least part of themolten material after curing the monomer.
 3. The method of claim 2,wherein the solidified at least part of the molten material forms ahandle, holder, or protective casing.
 4. The method of claim 1, whereinthe mould is positioned using a flotation device that is supported bythe molten material and that is configured to hold the mould in a setposition relative to the molten material.
 5. The method of claim 4,wherein the mould is adjustable in position relative to the flotationdevice.
 6. The method of claim 4, further comprising the step ofadjusting the position of the flotation device relative to the moltenmaterial by adding or removing ballast on the flotation device.
 7. Themethod of claim 1, wherein the step of adding the monomer is executedthrough ports in the mould and/or flotation device.
 8. The method ofclaim 7, wherein the mould and/or flotation device is tilted whilst themonomer is added.
 9. The method of claim 1, further comprising the stepof forming a surface pattern on the molten material prior to the curingof the monomer.
 10. The method of claim 9, wherein the surface patternis formed by way of an ultrasonic emitter.
 11. The method of claim 1,further comprising the step of embedding an object in the monomer, priorto curing.
 12. The method of claim 11, wherein the object is embedded onthe surface of the monomer or within the monomer.
 13. The method ofclaim 11, wherein the object is positioned by way of one or morespacers.
 14. The method of claim 1, further comprising the step ofpositioning, prior to curing of the monomer, a secondary mould thatbounds the mould cavity, the secondary mould being supported by themolten material.
 15. A system for forming a polymer, the systemcomprising: a bath containing a molten material; and a mould positionedin relation to the bath in order to form a mould cavity between themould and the molten material, for the receipt of a monomer.
 16. Thesystem of claim 15, further comprising a flotation device that issupported by the molten material and is configured to hold the mould ina set position relative to the molten material.
 17. The system of claim16, wherein the mould is adjustable in position relative to theflotation device.
 18. The system of claim 17, wherein the flotationdevice comprises a support structure including one or more joints toallow the adjustment of the position of the mould.
 19. The system ofclaim 15, further comprising ballast that is movable to adjust theposition of the flotation device relative to the molten material. 20.The system of claim 15, wherein the mould and/or flotation deviceinclude ports for the addition of the monomer.
 21. The system of claim15, further comprising a device configured to form a surface pattern onthe molten material.
 22. The system of claim 21, wherein the devicecomprises an ultrasonic emitter.
 23. The system of claim 15, furthercomprising a secondary mould that bounds the mould cavity, the secondarymould being supported by the molten material.